Methods and apparatus for balancing armatures during coil winding

ABSTRACT

The balance of rotors for dynamo-electric machines (e.g., electric motor armatures), which are wound with two diametrically opposite, simultaneously applied coils of wire, is improved by ensuring that wire is fed to both coils in substantially similar quantities. This can be accomplished by monitoring the lengths of the two wires as they are fed to the armature using wire sensors located adjacent to the flyer. Alternatively, wire sensors can be provided to monitor the rate at which wire is being fed towards respective flyers and to measure the rate of change of the lengths of those portions of the wires that are supported by the winding machine dancer arms. A control system processes the measurements from these sensors. A wire tensioner having a hysteresis clutch is also provided that allows the tension applied to a wire being wound to be adjusted rapidly. The wire tensioner also picks up slack that may develop in the wire.

This is a continuation-in-part of application Ser. No. 08/042,607, filedApr. 2, 1993, now U.S. Pat. No. 5,383,619.

BACKGROUND OF THE INVENTION

This invention relates to making armatures for dynamo-electric machinessuch as motors and generators. Although the invention will be describedprimarily in the context of its application to electric motor armatures,it will be appreciated that it is equally applicable to rotating rotorsin general which are wound with wire for conducting electric current.For convenience, all such rotors are referred to herein as armatures.Also, although the invention will be described primarily in the contextof flyer type armature coil winders, it will be understood that theinvention is equally applicable to winders that employ other types ofcoil wire dispensing members such as the apparatus shown in commonlyassigned U.S. Pat. No. 5,484,114.

As shown in FIG. 1, finished armatures 10 wound with wire 12 in coilreceiving slots 14 of a lamination stack 16 need to be preciselybalanced prior to their final operational use. This avoids mechanicalmalfunctioning, and also guarantees the integrity of the armature,together with that of other components which are assembled in theenvironment where the final operational use occurs.

It is common practice to use automatic balancing machines at the end ofan armature production line to determine how unbalanced the armature hasbecome during the processing stages and to correct for this unbalancedcondition by adding or removing masses on certain parts of the finishedarmature. The most common technique for automatic balancing of armaturesremoves masses by milling one or more grooves in the outercircumferential surface of the armature stack 16.

An unbalanced armature (requiring balancing as described above) may bethe result of an unbalanced stack 16, shaft 18, or commutator 19, andalso may be the result of the overall disposition of the masses of thesecomponents as a result of the operations required to assemble them toform the armature. An unbalanced armature can also result from theoperational steps required to wind the coils of wire 12 in the slots 14of stack 16. Although the disposition of the coils (and their number ofturns) around the armature is theoretically correct for avoiding anunbalanced condition, practice has shown that the winding process canunbalance the armature.

In order to reduce the need for or the required extent of a finalbalancing step in the manufacture of armatures, it is an object of thisinvention to balance the armature during winding.

Formation of armature coils requires simultaneous winding of two wiresin two pairs of slots which are symmetrically opposite one another asshown in accompanying FIG. 2. For example, coil 20 is wound in slot pair22, 23 symmetrically opposite to coil 21 which is simultaneously woundin slot pair 24, 25.

One of the fundamental production specifications for winding armaturesusually requires winding symmetrically opposite pairs of slots (such asthose referenced above) with the same number of turns of wire. As hasbeen mentioned, this creates a theoretical basis for balancing thearmature, although, as will be more fully described below, in practiceduring winding various factors can cause an unbalanced condition.

Armatures of the type shown in accompanying FIG. 1 are frequently woundwith a flyer type winder, although other types of winders (e.g., thoseshown in above-mentioned U.S. Pat. No. 5,484,114 which is herebyincorporated by reference herein)) are also known and are subject to thesame problems and solutions discussed herein. As shown in accompanyingFIGS. 3 and 4, the typical flyer type winder includes two oppositeflyers 30, 31 which can rotate around respective axes 32, 33 so thateach of them dispenses an associated wire 34, 35 coming from a wirespool 36, 37 into a respective pair of coil receiving slots 38, 39 and40, 41 aligned with prepositioned winding forms 42, 43. The windingforms are required to guide each wire into the coil receiving slots asthe wire leaves the associated flyer. The wires required to wind thecoils, prior to reaching the flyers from the wire spools, pass throughrespective tensioner devices 46, 47 which are supposed to guarantee thatpredetermined tensions are maintained on the wires during the variousoperations required to wind and form the leads of the armature. The twoflyers 30 and 31 rotate at the same time so that each of them forms acoil in respective pairs of slots which are symmetrically disposed onopposite sides of a central transverse axis 80 of the armature. Flyers30 and 31 are driven by independent motors 44, 45, which are controlledto rotate in unison so that both flyers reach, as precisely as possible,similar predetermined angular positions in time. In particular, the twoflyers start and terminate rotation at the same time so that both coilsare wound simultaneously with the same number of turns.

At any given instant of time during winding, a difference between thetension of the wires being wound by their respective flyers can resultin different elongation of the wires. In a comparison between the twoflyers, which are winding opposite coils at the same time, this leads tosupplying in certain instances different masses of wire intosymmetrically opposite pairs of slots of the armature (such as thoseshown in FIG. 4). This has an unbalancing effect on the armature. Inaddition, a coil wound with higher tension will have more compact turns,which influences the radial disposition of its mass (e.g., in relationto the central longitudinal axis 82 of the armature). This alsocontributes to the formation of unbalanced armatures if variations ofthis type exist between the opposite coils being formed at the same timeby the two flyers.

The foregoing considerations can be further illustrated with the aid ofaccompanying FIG. 5, in which certain features are somewhat exaggerated.The wires relating to a few coil turns for respective opposite coils 20,21 are shown. The turns of coil 21 are wound with higher tension, whichsubjects the wire to a greater amount of elongation for the same numberof turns. This causes coil 21 to have less wire mass and to be morecompact toward the central longitudinal axis 82 of the armature thancoil 20. It should be appreciated that the formation of the overallcoils of the armature requires a progressive build-up of wire turns andalso of different coils. Later-wound turns and coils surmountearlier-wound turns and coils so that the later-wound material isfarther away from central axis 82. As a result of this overlying oroverlapping, the presence of an internal coil which is less compacttends to amplify the lack of balance because it also affects the massdisposition of successive coils which will be positioned farther awayfrom the central longitudinal axis 82 of the armature.

One approach for balancing armatures is described in commonly assignedU.S. Pat. No. 5,383,619. As described in U.S. Pat. No. 5,383,619, oneway in which to balance an armature involves measuring the amount ofwire leaving each of the two wire spools during winding using encodersto determine the velocity or length of the wire. This measurementreveals approximately how much wire is being wound onto the armature byeach of the two flyers. If it is determined that more wire is beingwound onto the armature by one of the flyers than the other, than therate at which wire is delivered to each of the flyers can be adjusted.

As described in the above-mentioned U.S. Pat. No. 5,383,619, the wirethat is fed to the flyers is tensioned using wire tensioners such ashysteresis brakes. The brakes are adjusted to balance the amount of wirethat is being fed to each of the flyers by varying the tension eachbrake applies to the wire. For example, the retarding force on the wirebeing wound onto one coil could be increased, so that subsequently, lesswire is wound onto that coil.

With this arrangement, rotating encoders 60 for measuring wireconsumption are typically placed immediately adjacent to the spool 36,as shown in FIG. 6, which is a reproduction of FIG. 6 of theabove-mentioned U.S. Pat. No. 5,383,619. For each flyer, tensioningdevice 46 is typically placed downstream of encoder 60. After tensioningdevice 46, wire 34 runs over a pulley wheel 68 of a spring biased dancerarm 69 prior to reaching flyer 30.

The dancer arm 69 is primarily required during operations in which theflyer undergoes abrupt changes in rotation direction and speed. In thesesituations the dancer arm accommodates any abrupt tightening orloosening of the wire that may occur by resiliently pivoting about axle70 in the appropriate direction 71. Although the arrangement shown inFIG. 6 is satisfactory for balancing armatures in many situations, suchan arrangement does not account for the changes in the length of thewire between tensioning device 46 and flyer 30 due to motions of thedancer arm 69 that might occur under extreme tensioning conditions. As aresult, at any given time, the wire consumption measured by encoder 60may not represent the amount of wire that has actually been wound ontothe armature as accurately as might be desired.

Another arrangement for balancing armatures during coil winding is shownin FIG. 7, which is a reproduction of FIG. 11 of the above-mentionedU.S. Pat. No. 5,383,619. Using this approach, wire tension sensors 120and 121 are provided to measure the tension of the wire being wound ontothe armature by flyers 30 and 31. Although the arrangement of FIG. 7 canbe used to balance armatures by maintaining the wire tensions measuredby sensors 120 and 121 at the same level, tension sensors may not alwaysbe as precise as desired when operating at extremely high speeds.

One of the components of conventional winding machines is the wiretensioner. Typically, using the arrangement described in theabove-mentioned U.S. Pat. No. 5,383,619, two hysteresis brakes are usedto tension the wires as they are fed to respective flyers. Conventionalhysteresis brakes contain a stationary stator. A rotor is mounted withinthe stator for rotational motion. Current is supplied to the field coilsof the stator to produce a retarding torque between the stator and therotating rotor. A pulley attached to the rotor axis applies thisretarding torque to the wire. The magnitude of the retarding torque iscontrolled by varying the current to the stator.

To decrease the wire tension, for example, when it is desired to formlead connections to the commutator of an armature following coilformation, the control current is lowered. However, conventionalhysteresis brakes suffer from an effect known as "cogging," in which thetension applied by the brake remains high even after the control currenthas been lowered. The tension remains at this high level until the rotorhas been forcibly moved by the tension of the wire through an angulardistance equal to the distance between successive poles. Because thetorque remains high, the lead connections are exposed to a larger wiretension than is desired, which can prevent the lead connections frombeing formed properly.

In view of the foregoing, it is an object of the present invention toprovide improved methods and apparatus for balancing armatures duringthe process of winding.

It is another object of this invention to provide an improved hysteresisbrake for use as a wire tensioner that overcomes the effects of cogging.

SUMMARY OF THE INVENTION

These and other objects of the invention are accomplished in accordancewith the invention by providing an improved winding machine forbalancing armatures during the process of winding coils.

In one embodiment, the winding machine uses wire sensors adjacent to theflyers to determine the respective lengths of wire that are wound ontothe armature by each of the two flyers during a predetermined period oftime. Based on the relative lengths of the two wires wound onto thearmature, the tensions applied by wire tensioning units are adjusted toequalize the lengths of the wires wound onto the armature duringsubsequent time periods. In most circumstances the mass of each wirelength is essentially proportional to the wire's length, so thatequalizing the lengths equalizes the masses, thereby balancing thearmature. In a preferred embodiment, the predetermined period of time isthe amount of time necessary to wind a pair of coils.

Another embodiment of the winding machine of the present inventioninvolves the use of multiple wire and position sensors to even moreaccurately determine the relative masses of the wires wound onto thearmature. One pair of wire sensors is provided adjacent to the flyersand another pair is provided adjacent to the wire supplies. Thesesensors are used to determine the rate at which wire is being fedtowards the flyers at these locations as a function of time. A thirdpair of sensors is connected to the pivoting axes of the dancer arms, toallow the determination of the rate of change of the lengths of wiresupported by the respective dancer arms as a function of time. Optionalwire thickness monitors are used to measure the diameters of the wiresas they exit the wire supplies.

A wire winding machine control system--preferably microprocessorbased--is used to process the signals from the various sensors todetermine the respective masses of the two wire lengths that are woundonto the armature during a predetermined period of time. By comparingthe relative masses, the wire tension applied to each of the wires canbe adjusted to equalized these masses during subsequent windingoperations.

An improved hysteresis brake unit is provided that uses a rotatablestator, rather than the conventional stationary stator design. Becausethe stator is rotatable relative to the housing and the rotor, after thetorque control current supplied to the stator has been reduced, a motorcan be used to rotate the stator relative to the rotor by apredetermined amount, thereby overcoming the effects of cogging.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional armature which can bewound in accordance with this invention.

FIG. 2 is a simplified axial end view of the armature of FIG. 1 showingthe dispositions of the core slots and the related coils.

FIG. 3 is a simplified elevational view of a conventional two flyerwinding machine.

FIG. 4 is an enlarged view, partly in section, of the central portion ofFIG. 3.

FIG. 5 is a simplified perspective view, with certain features somewhatexaggerated, showing coil turns relating to opposite receiving slots ofthe armature which may be produced simultaneously by conventionalarmature winding apparatus.

FIG. 6 is a simplified perspective view of an illustrative armaturewinding apparatus as shown in FIG. 6 of U.S. Pat. No. 5,383,619.

FIG. 7 is a simplified axial view of an illustrative armature windingapparatus as shown in FIG. 11 of U.S. Pat. No. 5,383,619.

FIG. 8 is a simplified perspective view of one side of an illustrativearmature winding apparatus constructed in accordance with the presentinvention.

FIG. 9 is a simplified axial view of both sides of the illustrativearmature winding apparatus of FIG. 8.

FIG. 10 is a typical current-torque relationship for a hysteresis brake.

FIG. 11 is a simplified perspective view of one side of a furtherillustrative armature winding apparatus constructed in accordance withthe present invention.

FIG. 12 is a simplified axial view of both sides of the illustrativearmature winding apparatus of FIG. 11.

FIG. 13 is a schematic block diagram of an illustrative control systemconstructed in accordance with the present invention.

FIG. 14 is a simplified sectional side view of a hysteresis brake unitconstructed in accordance with the present invention.

FIG. 15 is an illustrative timing diagram of the speed of rotation of awinding machine flyer versus time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Equipment used with a first embodiment of the invention for a two flyerarmature winding machine is shown in FIGS. 8 and 9. The equipment shownin FIG. 8 is that required for the flyer 100, which is also shown on theleft side of FIG. 9. Similar equipment is provided for flyer 102 on theright side of FIG. 9.

As shown in FIGS. 8 and 9, wires 104 and 106 are supplied to flyers 100and 102 from left and right spools 108 and 110, respectively. From spool108, the wire leads to a wire tensioner 112. Wire tensioner 112 includesa pulley wheel 114 about which wire 104 is preferably wound for morethan 360°. Pulley wheel 114 has a central shaft mounted on supports ofthe machine frame (not shown) for rotation about axis 116. The centralshaft of pulley wheel 114 is rigidly connected to the input shaft of ahysteresis brake 118, which is capable of supplying variable drag torqueon pulley wheel 114 when the pulley wheel is turned in direction 119 tosupply wire to flyer 100. The drag torque provided by brake 118 can bevaried by adjusting the electric current that is applied to the coils ofthe brake. FIG. 10 shows a typical performance curve for the hysteresisbrake where current I is plotted against braking torque T. Brakes ofthis type are commercially available from Magtrol, Inc. of Buffalo, N.Y.Alternatively, wire tensioners of the type shown in commonly assignedU.S. Pat. No. 5,310,124 (incorporated by reference herein) can beemployed if desired. As shown at the right side of FIG. 9, wire 106passes through a wire tensioner 122, similar to that of wire tensioner112.

After wire tensioners 112 and 122, wires 104 and 106 run over pulleywheels 124 and 126 of spring biased dancer arms 128 and 130,respectively, prior to reaching flyers 100 and 102. The wire tensioners112 and 122 are used to ensure that wires 104 and 106 have sufficienttension to guarantee that the coils wound onto armature 132 aresufficiently compact. The wire tensioners also maintain control of thewires as they are drawn from the spools by rotation of the flyers.

The dancer arms are used to dampen the wire tension transients thataccompany certain flyer operations, such as the operations required toconnect wire leads to the commutator of armature 132. During theseoperations the flyers undergo abrupt changes in rotational direction andspeed. The dancer arms pivot to accommodate any sudden tightening orloosening of the wire. For example, dancer arm 128 pivots about axle134, shown in FIG. 8.

After passing pulley wheels 124 and 126, wires 104 and 106 pass throughpulley wheels 136 and 138 of wire sensors 140 and 142, respectively.Wire sensors 140 and 142 are used to monitor the amount of wire that iswound onto the armature by flyers 100 and 102. Using a suitable controlsystem, the amount of wire that is wound onto the armature by therespective flyers can be equalized to balance the armature.

As shown in FIG. 8, pulley wheel 136 is mounted to rotate about axis 144by mounting its central shaft to the winding machine frame (not shown).The central shaft of pulley 136 is linked by means of a mechanical jointto the rotatable input of a suitable transducer, such as an encoder 146.Encoder 146 can supply output signals representing the rotations ofpulley 136 about axis 144. For example, encoder 146 may produce anoutput pulse each time pulley 136 rotates by a predetermined amount.Wire 104 is preferably looped for more than 360° around pulley wheel 136and a pressure wheel (not shown) may press on the wire to ensure that itdoes not slip as it runs on the pulley wheel. Wire sensor 140 ispreferably located along the associated wire 104 downstream from thewire tensioner 112 and the dancer arm 128. Wire sensor 142 is preferablyof similar construction to that of wire sensor 140.

During winding, wire 104 and 106 travels through wire sensors 140 and142, respectively. Wire sensors 140 and 142 measure the amount of wirethat has been wound onto the coils of armature 132. The amount of wirethat has been wound onto the armature can be determined by using wiresensors 140 and 142 to measure rates of travel of the wires toward theirrespective flyers, or by measuring the length of wire consumed sincesome predetermined starting time, such as the beginning of winding ofthe pair of coils currently being wound.

In a preferred embodiment of the invention, the wire sensors are used todetermine the lengths of the wires that are wound onto each respectivecoil in a pair of coils. The lengths of the wires wound onto the coilsare compared to determine to what degree the wire tensioners 112 and 122should be adjusted. For example, if it is determined that the secondcoil has a longer length of wire wound onto it than the first coil, thenthe tension applied to the wire leading to the second coil can beincreased by increasing the retarding force applied to the wire withwire tensioner 122. When the next pair of coils is wound, the highertension for the second coil will cause less wire to be wound onto thesecond coil than was previously wound, thereby tending to balance thearmature.

The tension applied by wire tensioner 122 can be adjusted asappropriate, while the tension applied by wire tensioner 112 remains ata nominal value selected prior to winding. This type of arrangement issometimes referred to as a "master-slave" configuration, where wiretensioner 112 acts as the master and wire tensioner 122 acts as theslave. Of course, wire tensioner 122 could be the master and wiretensioner 112 the slave, if desired. It is also possible tosimultaneously adjust the tension applied by both wire tensioners 112and 122.

Any suitable algorithm for adjusting the tensions applied by thesedevices can be employed. For example, the tension applied by one of thewire tensioners (the slave) can be increased or decreased in a linearfashion, based on the measured difference in wound coil lengths, asshown in Equation 1.

    New·Tension=Old·Tension+c * (X.sub.L -X.sub.R)(1)

In Equation 1, New·Tension is the tension to be applied by the slavewire tensioner when the next pair of coils is wound. Old·Tension is thetension that was previously applied. X_(L) and X_(R) are the values ofwire length measured by the wire sensors 140 and 142, respectively. Theconstant c is determined empirically. The value of c will typicallydepend on the type of armature being wound and the size andcharacteristics of the wire being used. Equation 1 is one suitableexpression for determining the tension to be applied by the slave wiretensioner. It is also possible to use an expression that has aquadratic, cubic, or higher order dependency on the measured differencein wire lengths. A set of two expressions similar to Equation 1 (or itsquadratic or higher order variants) can also be used if the tensionsapplied by both wire tensioners 112 and 122 are to be adjusted. Thealgorithm used to adjust the wire tensioners can be implemented by thecontrol system of the winding machine using an equation such as Equation1 stored either as a set of instructions to be executed by, e.g., amicroprocessor, or as a look-up table stored in a suitable memorydevice.

The purpose of making the periodic adjustments to the wire tensioners112 and 122 (preferably once per coil pair) is to is to reduce andultimately substantially eliminate the difference between the lengths ofthe wires that are wound onto the armature to form the coils. This alsotypically has the effect of at least eventually reducing tensiondifferences between the two wires. Equalizing the lengths (and thereforetensions) of the two wires wound onto the armature reduces differenceswhich would exist in the two coil masses being wound, and also producesa similar compactness in the two coils. As has been described above,this balances opposing coils and thus the entire armature.

The winding machine arrangement shown in FIGS. 8 and 9 and describedabove is superior to previously-known winding machines because the wiresensors 140 and 142 are placed directly adjacent to the flyers, with nointervening tensioning equipment. The measured wire length moreaccurately reflects the mass of the wire that has been wound onto thearmature, because when dancer arms 128 and 130 pivot a different amountof wire may be wound onto the armature than would be detected bymeasuring the wire consumption in the vicinity of the spool. Becausewire sensors 140 and 142 are directly adjacent to the flyers 100 and102, the actual length of wire wound onto the armature is measured.

Under extreme wire tensions, the motions of the dancer arms 128 and 130and transients in the tensions of the wires as they are wound onto thearmature can adversely affect the accuracy of the determination of therespective masses of the coils that are ultimately formed on thearmature, even if the wire sensors are located adjacent to the flyer.This is because as the tension applied to the wire varies, the degree towhich the wire is elongated varies. The more the wire is elongated, thelower its linear mass. Thus, even if the length of wire wound onto thearmature is determined accurately, if the linear mass of the wire variessignificantly, it may not be possible to determine the wire mass asaccurately as desired using the winding apparatus of FIGS. 8 and 9.

As shown in FIGS. 11 and 12, further wire sensors can be provided toallow both the amount of wire wound onto the armature and the linearmass of the wound wire to be determined. As with the winding machinearrangement of FIGS. 8 and 9, two similar sets of equipment are used,one for each of the flyers 148 and 150. The equipment in FIG. 11 is usedfor flyer 148.

Spool 152 supplies wire, whose diameter can be measured using anoptional wire thickness gauge 154. Wire thickness gauges are well known.A typical gauge contains a source of illumination, such as a laser,which produces a beam of light perpendicular to the wire. The wirepassing through the gauge intersects the beam allowing the diameter ofthe wire to be determined.

A wire sensor 156 measures the amount of wire that is supplied from thespool. Wire sensor 156 operates similarly to wire sensor 140 (FIG. 8).Wire sensor 156 is used to periodically measure the rate of travel ofthe wire toward the flyer. After wire sensor 156, the wire passes thoughwire tensioner 158, which can be constructed similarly to that of wiretensioner 112 (FIG. 8).

The wire passes through pulley wheel 160 of dancer arm 162, which is ofthe same type as dancer arm 128 (FIG. 8). Dancer arm 162 pivots aboutthe axis of shaft 164 to accommodate abrupt changes in the tension ofthe wire. A position sensor having an encoder 166 can be used todetermine the rotational position of dancer arm 128. After pulley wheel160 the wire passes to flyer 148 via wire sensor 168, which ispreferably constructed similarly to wire sensor 156. The winding machineparts shown on the right side of FIG. 12--spool 170, wire gauge 172,wire sensor 174, wire tensioner 176, encoder 177, dancer arm 178, andwire sensor 180--are used with flyer 150.

The addition of wire sensor 156 and encoder 166 allow the mass of thewires wound onto the armature to be accurately determined, even ifextreme wire tensions and large movements of the dancer arms 162 and 178are encountered. The mass of any segment of wire wound onto the coil isequal to the linear mass (mass per unit length) of the wire integratedover the length of the wire segment. Because the wire elongates undertension, the linear mass of wire that has been tensioned is less thanthe wire emerging from the spool. As shown in FIG. 11, wire segment 182,which extends from spool 152 to wire tensioner 158, is relativelyuntensioned. Between the wire tensioner 158 and the armature 186, wiresegment 184 is tensioned by the actions wire tensioner 158, dancer arm162 and flyer 148.

Although the linear mass of the wire changes under tension, overall massis conserved. The principal of conservation of wire mass is embodied inEquation 2.

    G1(t) V1(t)=G2(t) (V2(t)+VD(t))                            (2)

In Equation 2, G1 is the linear mass of wire segment 182 and G2 is thelinear mass of wire segment 184. V1 and V2 are the velocities of thewire at the wire sensors 156 and 168, respectively. The variable VD isthe rate of change in the length of the portion of wire segment 184 thatis between wire tensioner 158 and wire sensor 168 (i.e. the change inthe length of the wire supported by the dancer arm 16 per unit time).

The total mass of a wire segment that is wound onto the armature, M, isgiven by Equation 3, where T is the period of time taken to wind thewire segment onto the armature. ##EQU1## As described below, the valuesof G1, V1, V2, and VD are known, so that the value of G2 can be obtainedfrom Equation 2. The total mass of the wire segment wound onto thearmature can then be obtained from Equation 3. By comparing the masswound onto the armature by flyer 148 to that of the mass wound by flyer150, the wire tensioners 158 and 176 can be adjusted appropriately tobalance the armature.

The values of G1, V1, V1, and VD can be determined using the varioussensors shown in FIG. 11. As the flyer draws wire from spool 152, thelinear mass of wire segment 184 may vary slowly due to variations in thediameter of the wire. These variations can be sensed by the wirethickness gauge 154 to determine the value of G1 as a function of time.Alternatively, because the nominal wire diameter does not varysubstantially, G1 can be assumed to be a constant.

The value of V1 can be obtained from the wire sensor 156. Similarly, thevalue of V2 can be obtained from the wire sensor 168. The rate of changein the length of the wire segment supported by the dancer arm, VD, canbe determined based on the known length of that wire segment as afunction of the position of dancer arm 162 and the measured value ofthat position, which is provided by encoder 166.

The equipment shown in FIG. 11 and on the left of FIG. 12 is used withflyer 148 to wind the wire onto the armature and to determine the totalmass of any given segment of wire that is wound. The components on theright side of FIG. 12 are used to perform the same functions with flyer150. By periodically comparing the total masses of the respective wiresegments that have been wound onto the armature, the wire tensioners canbe periodically adjusted to equalize the masses delivered to opposingarmature coils, thereby balancing the armature.

Any suitable algorithm can be used to adjust the wire tensions providedby wire tensioners 158 and 176. For example, a linear algorithm, such asthat defined by Equation 1, or a quadratic or higher order algorithm canbe used. The coefficients for the various terms in the algorithm can bedetermined empirically for various wire and armature types. One suitablealgorithm for determining to what extent the wire tensioners 158 and 176should be adjusted is given by Equations 4 and 5.

    TR=T0+k * (MR-ML)/(MR+ML)                                  (4)

    TL=T0-k * (MR-ML)/(MR+ML)                                  (5)

In Equations 4 and 5, MR and ML are the respective masses of twoopposing wire segments that have been wound onto the armature. Themeasurements necessary to determine MR and ML are made using the sensorsshown on the right and left of FIG. 12, respectively. The windingmachine control system determines MR and ML based on these measurementsusing Equation 3. TR and TL are the tensions to be applied by wiretensioners 158 and 176 in response to the values obtained for MR and ML.T0 is the nominal tension value, one which has been shown to generallyproduce satisfactory results. The constant k can be determinedempirically for various combinations of wire type and armatures.

Similarly, a suitable winding machine arrangement such as the machineshown in FIGS. 8 and 9 can also use a torque adjustment algorithm basedon Equations 4 and 5, if desired. With such an arrangement, sensors 140and 142 can be used to monitor the wire lengths that are wound ontosuccessive coils. After winding each pair of coils, the measured lengthscan be compared. The respective tensions to be applied to the wires whenwinding the next set of coils can then be adjusted with wire tensioners112 and 122 using Equations 4 and 5.

Any suitable control system may be used to perform the processingnecessary to determine the masses of respective wire segments from thesensor readings and to control the operation of the winding machine. Forexample, dedicated circuitry could be used. Another suitable controlsystem design is based on a microprocessor. An illustrativemicroprocessor-based control system is shown in FIG. 13. Control system188 uses microprocessor 190 to execute instructions loaded into memory192. By executing the appropriate instructions, microprocessor 190processes the signals from the various winding machine sensors andimplements the control routines necessary to balance the armature duringwinding.

If the wire sensors used to measure the amount of wire being wound ontothe armature are of the type that produce a certain number of digitalpulses per revolution of a pulley wheel, these pulses must be processed.One suitable approach for processing these sensor signals is to countthe signals from the wire sensor encoders per unit time, therebyallowing the control system 188 to determine the necessary wirevelocities.

For example, the pulses from encoders 194, 196, 198, 200, 202, and 204can be counted by counters 206, 208, 210, 212, 214, and 216,respectively. If a sensor arrangement such as that shown in FIGS. 11 and12 is used, six counters can be used to count the various signal pulsesfrom the six encoders 218, 166, 220, 222, 177, and 224. Data from thecounters is provided to the microprocessor 190 via bus 226. Themicroprocessor 190 can process the counter data to determine thevelocities V1, V2, and VD.

If the sensor arrangement is similar to the arrangement shown in FIGS. 8and 9, then two counters can be used to count the signal pulses fromencoders 140 and 142. The microprocessor 190 can then process thecounter data to determine the length of wire that has been drawn pasteach wire sensor.

The output of the wire gauges 154 and 172 can be provided tomicroprocessor 190 via a suitable interface device 228. Interface device228 can be, for example, a multi-channel analog-to-digital converterthat receives the outputs from wire gauges 154 and 172 at inputs 230 and232, respectively. Alternatively, interface device 228 can be a digitalinterface capable of receiving digital signals from the wire gauges thatare indicative of the measured wire thicknesses.

Another signal that may be provided to the microprocessor 190 is aposition signal from one of the flyer drives. For example, flyer drive234 (FIG. 9) can provide a position signal at output 236 or flyer drive238 can provide a position signal at output 240. The position signalfrom the flyer drive, which is indicative of flyer rotation or angularposition, can be provided to microprocessor 190 via a suitable interfacedevice 242.

The control system 188 processes the signals from the various sensorsand determines the magnitude of any adjustments to be made to thetensions that are applied by the wire tensioners using any suitablealgorithm, as described above. The control system 188 generatescorresponding digital control signals, which are provided todigital-to-analog converters 244 and 246. Digital-to-analog converters244 and 246 convert the digital control output signals to the analogform typically required by wire tensioners such as hysteresis brakes 248and 250, to modify the torque they apply and thereby adjust the tensionof the wires. Prior to being supplied to the brakes, these signals canbe amplified by amplifiers 252 and 254.

Line 256 can be used for entering ideal wire tensions, e.g., usingpotentiometers to supply analog signals that are transformed to digitalsignals for microprocessor 190.

Lines 258 can make up a serial link coming from a host or remotecontroller which can be the winder's ultimate controller, so that whensetting the winder for a particular type of armature, the ideal tensionis automatically transferred to microprocessor 190 without requiring anyfurther local input. Keyboard and monitor 260 are alternative inputdevices which an operator can use to supply the required tensionconditions.

Although the wire and position sensors that have been described haveencoders to generate a number of output pulses per revolution that canbe counted by respective counters, any suitable sensor arrangement forsensing the amount of wire consumed or the position of the dancer armcan be used. For example, sensors can be provided that contain countersand processing circuitry. If the sensors contain such additionalcircuitry, the signals transmitted from the sensors to the controlsystem 188 are more directly indicative of the parameter being measured.A wire sensor output might be an analog or digital signal having a valueequal to the length of wire consumed or the velocity of the wire.Similarly, a position sensor for determining the position of the dancerarm could provide an analog or digital output signal that indicates theposition and velocity of the dancer arm. Further, although the countersin FIG. 13 are shown connected to microprocessor 190 via bus 226, theanalog or digital output signals from the various sensors couldalternatively be supplied to microprocessor 190 via suitable interfacecircuitry 262.

Similarly, although the wire gauge sensors, the flyer drivers, thecircuitry for entering the wire tension, the host, and the keyboard andmonitor are shown connected directly to the microprocessor 190, theoutputs of some or all of these can be provided to microprocessor 190via suitable interface circuitry 264 connected to bus 226, if desired.

Another aspect of the present invention relates to improvements to thewire tensioning arrangement used to tension the wire as it is wound ontoa wound electric motor component (e.g., a rotor or stator) for adynamo-electric machine. As described above, one suitable type of wiretensioner is based on a hysteresis brake. Typically, hysteresis brakeshave an axle connected to a rotor that rotates within a stationarystator. By varying the current supplied to the field coils of thestator, a variable torque is applied to the axle.

The hysteresis brakes used with the wire winding machines describedabove have pulley wheels about which wire to be tensioned is wound. Asthe flyer draws wire past the hysteresis brake, the pulley wheelrotates. When a current is supplied to the field coils of the stator, aretarding torque is generated by the brake. The torque applied by thebrake is a function of the current supplied to the brake, generallyfollowing the relationship shown in FIG. 10.

However, it is often difficult to use hysteresis brakes for wiretensioning in a winding machine. During the process of winding, it isoften necessary to quickly reduce the torque applied by the brake. Forexample, when a coil has been wound and the flyer stops rotating inorder to form lead connections, the torque generated by the brake mustbe reduced prior to forming the lead connections so that the leadconnections can be formed properly.

It is not possible, however, to simply reduce the current that issupplied to the stator at this point, because hysteresis brakes sufferfrom a phenomenon known as "cogging," in which the torque applied by thebrake remains high, even after the controlling current has been reduced.The cogging phenomenon is well known. Because of this phenomenon, thetorque applied by the brake will not decrease to the desired level untilthe rotor has rotated at least a certain angle relative to the stator.Generally, the rotor must rotate an angle of rotation equal to theangular separation between two poles. Because the torque remains highdue to cogging, as the lead connections are formed, they are exposed toa larger wire tension than is desired, which can prevent the leadconnections from being formed properly or which can cause the wire tobreak.

In accordance with the present invention, a wire tensioner 266 isprovided having a hysteresis clutch 268, as shown in FIG. 14.Preferably, hysteresis clutch 268 is a clutch such as a clutch in theHCS series of clutch models available from Magtrol Inc. of Buffalo, N.Y.Hysteresis clutch 268 has a rotor 270 that is connected to an axle 272,which is rotatably mounted in stationary housing 274. A pulley 276 orsimilar member for engaging wire 278 is connected to axle 272.

Clutch 268 receives a controlling current via input 282. Rotating stator280 is rotated relative to the stationary housing 274 by motor 284 usingaxle 281. The actual speed of rotation of the rotating stator 280 ispreferably reduced from the speed of rotation of the motor 284 byreduction gear 283. Preferably motor 284 is a fixed speed AC motor thatreceives a drive voltage via input 290. Pulley 276 typically rotates soas to feed wire toward the electric motor component to be wound.Rotating stator 280 rotates in the opposite direction.

The hysteresis clutch 268 provides a retarding torque to the pulleywheel 276. The magnitude of the retarding torque is primarily determinedby the value of the current applied to the hysteresis clutch 268 viainput 282. By varying the current supplied to input 282, the wire 278can be tensioned as desired.

When it is desired to lower the torque applied by wire tensioner 266,the current supplied to input 282 is reduced to the desired level. Usingreduction gear 283 and axle 281, motor 284 rotates rotating stator 280relative to rotor 270 by an angular amount that is preferably sufficientto overcome the effects of cogging. The torque produced by thehysteresis clutch 268 is therefore immediately reduced to a valuecorresponding to the reduced current level. The ability to rapidly lowerthe torque applied to the wire precisely when desired allows theretarding torque provided by pulley wheel 276 to be reduced prior to theportion of the winding process that involves forming lead connections.Thus, the tension of the wire during winding can be controlled with thewire tensioner 266 to avoid undesirable high tensions that previouslyoccurred during the lead connection process.

The speed of rotation of a typical winding machine flyer during theprocess of winding an armature is shown in FIG. 15. During time periodT1, the flyer winds wire onto a first armature coil. During time periodT2, the flyer is stationary while the winding machine moves theappropriate lead connection point into position. As described above, itis desired that the torque applied to the wire during the process offorming lead connections be relatively low. Accordingly, during periodT2, the current supplied to the wire tensioner 266 via input 282 isreduced. The rotation of motor 284 causes the rotating stator 280 torotate relative to rotor 270, which eliminates the effects of cogging.The torque applied by the wire tensioner 266 during period T2 thereforequickly drops to a relatively low level. During time period T3, thewinding machine performs various lead connection operations. (As shownin FIG. 15, during time period T3 the direction of rotation of the flyermay reverse.) Because the torque applied by wire tensioner 266 waslowered during period T2, the lead connections during period T3 can beformed without deforming the lead connections (e.g., without bending thetangs of a commutator). Another winding cycle, in which a second coil iswound, begins with time period T4. An advantage of this approach is thatrotation of the rotating stator 280 by motor 284 can be accomplishedduring period T2 prior to the lead connection step. No additional timeis required to complete the winding cycle.

As described above, a significant advantage of using hysteresis clutch268 in wire tensioner 266 is that the motor 284 can be used to rotatethe rotating stator 280 relative to the rotor 270 to overcome theeffects of cogging. Another significant advantage of using hysteresisclutch 268 in wire tensioner 266 is that the direction of rotation ofthe pulley wheel 276 can be reversed to pick up slack that may developat certain stages in the winding process.

During most winding operations, the pulley wheel is rotated in a forwarddirection by the force of the wire being drawn past it towards theelectric motor part being wound (e.g, the armature or stator), while themotor 284 rotates the rotating stator in the opposite direction.However, occasionally it is desirable to for the direction of the pulleywheel to reverse, in order to pick up slack that has developed in thewire and to maintain an appropriate tension on the wire. For example,during certain stages of armature winding, the motion of the flyer maycreate slack in the wire between the pulley wheel and the armature. Whenthis occurs, the retarding torque applied to the pulley wheel 276 by thehysteresis clutch 268 causes the pulley wheel to reverse its directionof rotation, while the motor 284 continues to rotate the rotating stator280, so that instead of allowing slack to develope in the wire, thepulley wheel draws wire back from the armature. During winding, thetorque applied to the pulley wheel 276 by hysteresis clutch 268 can beincreased or decreased by increasing or decreasing the current appliedto the clutch 268, if desired. Typically, dancer arms are providedupstream from the pulley wheel to recover any wire that is drawn backfrom the direction of the wound motor component.

Another situation in which slack may develop in the wire being woundonto the electric motor component occurs during stator winding. Roboticwire manipulation devices are typically used to position the ends of thecoil leads as they are connected to terminals on stators or anchoringpoints on workpiece holders. These robotic manipulators position wiresin a way that makes it desirable to be able to draw wire back towardsthe pulley wheel. The retarding torque applied to the pulley wheel 276causes the direction of rotation of the pulley wheel to reverse wheneverwire slack develops, while motor 284 continues to rotate the rotatingstator 280. Further, during the process of forming lead connections tostator terminals, it may be desirable to increase the retarding torqueso that, in addition to removing slack from the wire, a sufficienttension is developed in the wire to form a tight lead connection. Thiscan be accomplished by increasing the value of the control current tothe hysteresis clutch 268 at the appropriate time during the leadconnection process. The increased control current increases the torqueapplied to the pulley wheel 276 by the hysteresis clutch 268, so thatthe knot can be formed as desired.

If wire tensioner 266 uses a hysteresis clutch, the hysteresis clutch268 is preferably controlled by control system 188 (FIG. 13).Microprocessor 190 executes instructions stored in memory 192 thatdirect the microprocessor to generate appropriate digital motor controlsignals, which are provided to digital-to-analog converter 286. Theanalog output of digital-to-analog converter 286 can be amplified by anamplifier 288, if desired. The output of amplifier 288 is preferably ananalog control signal that can be used to control the torque applied topulley wheel 276 by hysteresis clutch 268, by supplying a suitable inputcontrol current at input 282, as shown in FIG. 14. If desired, a similardigital-to-analog converter and amplifier may be provided to generatethe control voltage applied to input 290 of motor 284 (FIG. 14).

It will be understood that the foregoing is merely illustrative of theprinciples of this invention, and that various modifications can be madeby those skilled in the art without departing from the scope and spiritof the invention. For example, although the invention has beenillustrated in the context of flyer type winders, the invention isequally applicable to winders having other types of wire dispensingmembers such as those shown in above-mentioned U.S. Pat. No. 5,413,289.Similarly, although the use of hysteresis brakes has been described,other types of wire tensioners (e.g., those shown in above-mentionedU.S. Pat. No. 5,310,124) are known and can be employed if desired.

The invention claimed is:
 1. Apparatus for simultaneously winding twocoils of wire onto a rotor for use in a dynamo-electric machinecomprising:first and second wire supplies for respectively supplyingfirst and second wires; first and second winders for respectivelywinding said first and second wires onto said rotor; first and secondmeans for respectively monitoring the lengths of said first and secondwires that are wound onto said rotor during a predetermined period oftime; first and second means for respectively applying tension to saidfirst and second wires; and means responsive to said first and secondmeans for monitoring for adjusting the tension applied by at least oneof said first and second means for applying tension in order tosubstantially equalize the lengths of said first and second wires woundonto said rotor during a subsequent one of said predetermined periods oftime, wherein said first and second means for monitoring arerespectively downstream along said first and second wires from saidfirst and second means for applying tension.
 2. The apparatus defined inclaim 1 wherein said predetermined period of time is the length of timenecessary to wind said two coils.
 3. The apparatus defined in claim 1wherein said first and second means for applying tension compriserespective first and second hysteresis brakes.
 4. The apparatus definedin claim 1 wherein said first and second means for monitoringrespectively comprise:first and second rotatable members respectively incontact with said first and second wires so that each of said first andsecond members rotates at a rate indicative of the rate at which thewire in contact with it is passing; and first and second digitalencoding means respectively associated with said first and secondrotatable members so that each of said first and second encoding meansproduces an output signal pulse each time the associated rotatablemember rotates by a predetermined amount.
 5. The apparatus defined inclaim 4 wherein said means for adjusting comprises:means responsive tothe output signal pulses produced by said first and second digitalencoding means for detecting any difference between the numbers ofoutput signal pulses produced by said first and second digital encodingmeans.
 6. The apparatus defined in claim 5 wherein, when said means fordetecting detects a difference between the numbers of output signalpulses produced by said first and second digital encoding means, saidmeans for detecting identifies which of said first and second digitalencoding means has produced more of said output signal pulses, andwherein said means for adjusting further comprises:means for producing arelative increase in the tension of the wire associated with the digitalencoding means that has produced more of said output signal pulses. 7.Apparatus for simultaneously winding two coils of wire onto a rotor foruse in a dynamo-electric machine comprising:first and second wiresupplies for respectively supplying first and second wires; first andsecond winders for respectively winding said first and second wires ontosaid rotor during a predetermined time period, thereby forming first andsecond wire masses on said rotor; first and second means forrespectively applying tension to said first and second wires as saidfirst and second wires pass said first and second means for applyingtension, wherein said first and second means for applying tension aredownstream along said wires from said first and second wire supplies andare upstream from said first and second winders; first and second meansfor respectively monitoring the rates at which said first and secondwires are fed toward said first and second winders past said first andsecond means for monitoring, wherein said first and second means formonitoring are respectively downstream along said wires from said firstand second means for applying tension; third and fourth means forrespectively monitoring the rates at which said first and second wiresare fed toward said first and second winders past said third and fourthmeans for monitoring, wherein said third and fourth means for monitoringare respectively upstream along the wires from said first and secondmeans for applying tension; first and second means for respectivelyfurther tensioning said first and second wires, said first and secondmeans for further tensioning respectively supporting first and secondlengths of said first and second wires, wherein said first and secondmeans for further tensioning are respectively upstream along said wiresfrom said first and second means for monitoring and are downstream fromsaid first and second means for applying tension; fifth and sixth meansfor respectively monitoring the rate of change of said first and secondlengths of said wires supported by said means for further tensioning;and means responsive to said first, second, third, fourth, fifth, andsixth means for monitoring for adjusting the tension applied by at leastone of said first and second means for applying tension in order tosubstantially equalize said first and second wire masses during asubsequent one of said predetermined periods of time.
 8. The apparatusdefined in claim 7 wherein said predetermined period of time is thelength of time necessary to wind said two coils.
 9. The apparatusdefined in claim 7 wherein said first and second means for applyingtension comprise respective first and second hysteresis brakes.
 10. Theapparatus defined in claim 7 wherein said first and second means formonitoring respectively comprise:first and second rotatable members inrespective contact with said first and second wires so that said firstand second members rotate at rates indicative of the respective rates atwhich the first and second wires are passing said first and secondrotatable members; and first and second digital encoding meansrespectively associated with said first and second rotatable members sothat said first and second digital encoding means produce respectiveoutput signal pulses each time the first and second rotatable membersrotate by a predetermined amount.
 11. The apparatus defined in claim 10wherein said third and fourth means for monitoring respectivelycomprise:third and fourth rotatable members in respective contact withsaid first and second wires so that said third and fourth members rotateat a rate indicative of the respective rates at which the first andsecond wires are passing said third and fourth rotatable members; andthird and fourth digital encoding means respectively associated withsaid third and fourth rotatable members so that said third and fourthdigital encoding means produce respective output signal pulses each timethe third and fourth rotatable members rotate by a predetermined amount.12. The apparatus defined in claim 11 wherein said first and secondmeans for further tensioning respectively comprise:first and seconddancer arms mounted for pivoting about respective first and second axes,said first and second dancer arms having respective first and secondpulleys for engaging said first and second wires.
 13. The apparatusdefined in claim 12 wherein said fifth and sixth means for monitoringrespectively comprise:fifth and sixth digital encoding meansrespectively associated with said first and second dancer arms so thatsaid fifth and sixth digital encoding means produce respective outputsignal pulses each time the first and second dancer arms pivot aboutsaid first and second axes by a predetermined amount.
 14. The apparatusdefined in claim 7 wherein said means for adjusting furthercomprises:means for producing a relative increase in the tension of thewire associated with the larger of the two wire masses.
 15. Theapparatus defined in claim 7 further comprising a wire thickness gaugeadjacent to each wire supply for determining the diameters of the firstand second wires.
 16. A method for simultaneously winding two coils ofwire onto a rotor for use in a dynamo-electric machine, each of saidcoils being wound by a respective one of first and second windersrespectively supplied with first and second wires from first and secondwire supplies, said method comprising the steps of:applying tension tosaid first and second wires with first and second wire tensioners;monitoring the respective first and second lengths of said first andsecond wires that are wound onto said rotor during a predetermined timeusing respective first and second wire monitors, said first and secondwire monitors being located between said respective first and secondwire tensioners and said respective first and second winders; andadjusting the tension applied by at least one of said wire tensioners toequalize the first and second lengths of said wire that are wound ontosaid rotor during a subsequent predetermined period of time.
 17. Themethod defined in claim 16 wherein said predetermined period of time isthe length of time necessary to wind said two coils.
 18. The methoddefined in claim 16 wherein said step of applying tension comprises thestep of applying tension with first and second hysteresis brakes. 19.The method defined in claim 18 wherein said step of monitoring therespective first and second lengths comprises the step of:allowing firstand second rotatable members in respective contact with said first andsecond wires to rotate so that said first and second members rotate atrespective first and second rates that are indicative of the respectiverates at which the first and second wires are passing said first andsecond rotatable members; and encoding said first and second respectiverates associated with said first and second rotatable members to producean output signal pulse each time an associated rotatable member rotatesby a predetermined amount.
 20. The method defined in claim 19 whereinthe step of adjusting the tension comprises the steps of:processing theoutput signal pulses to determine said first and second lengths of saidwire; comparing said first and second lengths of wire; and increasingthe tension applied to the wire corresponding to the longer of saidfirst and second lengths.
 21. A method for simultaneously winding twocoils of wire onto a rotor for use in a dynamo-electric machine,comprising the steps of:supplying first and second wires from first andsecond wire supplies; winding said first and second wires onto saidrotor using respective first and second winders for a predetermined timeperiod, thereby forming corresponding first and second wire masses onsaid rotor; applying tension to said first and second wires with firstand second wire tensioners; monitoring first and second respective ratesat which said first and second wires are fed toward said first andsecond winders using respective first and second wire monitors locatedrespectively between said first and second wire tensioners and saidfirst and second winders; monitoring third and fourth respective ratesat which said first and second wires are fed toward said first andsecond winders using third and fourth wire monitors located respectivelybetween said first and second wire tensioners and said first and secondwire supplies; further tensioning a first length of said first wirebetween said first wire tensioner and said first wire monitor and asecond length of said second wire between said second wire tensioner andsaid second wire monitor, said first length of wire having a fifth rateof change of length and said second length of wire having a sixth rateof change of length; monitoring said fifth and sixth rates; andadjusting the tension applied by at least one of said wire tensionersbased on said monitored first, second, third, fourth, fifth, and sixthrates to equalize subsequently formed ones of said first and second wiremasses.
 22. The method defined in claim 21 wherein said predeterminedperiod of time is the length of time necessary to wind said two coils.23. The method defined in claim 22 wherein the step of applying tensionto said first and second wires comprises the step of applying tensionwith respective first and second hysteresis brakes.
 24. The methoddefined in claim 23 wherein the step of monitoring said first and secondrates comprises the step of:allowing first and second rotatable membersin respective contact with said first and second wires to rotate atrespective first and second rates that are indicative of the rates atwhich the first and second wires are passing said first and secondrotatable members; and encoding said first and second respective ratesassociated with said first and second rotatable members to produce anoutput signal pulse each time the first and second rotatable membersrotate by a predetermined amount.
 25. The method defined in claim 24wherein the step of monitoring said third and fourth rates comprises thestep of:allowing third and fourth rotatable members in respectivecontact with said first and second wires to rotate at respective thirdand fourth rates that are indicative of the rates at which the first andsecond wires are passing said third and fourth rotatable members; andencoding said third and fourth respective rates associated with saidthird and fourth rotatable members to produce an output signal pulseeach time the third and fourth rotatable members rotate by apredetermined amount.
 26. The method defined in claim 25 wherein thestep of further tensioning said wire comprises the step of supportingsaid first and second lengths of wire on respective pulleys mounted onfirst and second dancer arms.
 27. The method defined in claim 26 whereinthe step of monitoring the fifth and sixth rates comprises the step ofmonitoring the fifth and sixth rates with respective fifth and sixthdigital encoders so that said fifth and sixth digital encoders producerespective output signal pulses each time the first and second dancerarms pivot by a predetermined amount.
 28. The method defined in claim 27wherein the step of adjusting the tension comprises the stepsof:processing the output signals pulses to determine the first andsecond wire masses; and increasing the tension applied to the wirecorresponding to the larger of the first and second wire masses.
 29. Themethod defined in claim 21 further comprising the step of measuring thewire diameters of said first and second wires as said first and secondwires respectively exit said first and second wire supplies.